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Issuance of Policy Memorandum, In-Flight Operation of Propellers at Pitch Settings Below the Flight Regime for 14 CFR Part 23/CAR 3 Airplanes

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Federal Aviation Administration, DOT.


Notice of policy statement.


This document announces an FAA general statement of policy for certification of normal, utility, acrobatic, and commuter category turbine powered airplanes with propeller beta mode pitch settings.

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Randy Griffith, Federal Aviation Administration, Small Airplane Directorate, Regulations and Policy Branch, ACE-111, 901 Locust, Room 301, Kansas City, Missouri 64106; telephone (816) 329-4126; fax (816) 329-4090; email: <>.

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This notice announces the following policy statement, ACE-00-23.1155-01. The purpose of this statement is to address certification of normal, utility, acrobatic, and commuter category turbine powered airplanes with propeller beta mode pitch settings.

What Is the General Effect of This Policy?

The FAA is presenting this information as a set of guidelines suitable for use. However, we do not intend that this policy set up a binding norm; it does not form a new regulation and the FAA would not apply or rely on it as a regulation.

The FAA Aircraft Certification Offices (ACO's) and Flight Standards District Offices (FSDO's) that certify changes in type design and approve alterations in normal, utility, and acrobatic category airplanes should try to follow this policy when appropriate. Applicants should expect the certificating officials would consider this information when making findings of compliance.

As with all advisory material, this statement of policy identifies one way, but not the only way, of compliance.

General Discussion of Comments

Has FAA Taken Any Action to This Point?

We issued a notice of policy statement, request for comments. This proposed policy appeared in the Federal Register on September 1, 2000 (65 FR 53340) and the public comment period closed October 2, 2000.

Was the Public Invited To Comment?

The FAA encouraged interested people to join in making this proposed policy. We received comments from 5 different commenters. Commenters included manufacturers and aviation regulatory authorities.

Two commenters did not provide recommendations specific to the policy. The first agreed with the content. The second provided information and safety concerns on the possible rulemaking discussed in the background to the policy. We have noted the second's comment, which will be considered if we determine that rulemaking should be pursued.

Two commenters recommended that FAA consider for part 23 the material that was recently prepared for 14 CFR part 25 under the Powerplant Installation Harmonization Working Group (PPIHWG), as the same risks and considerations apply. We disagree that the same risks and considerations for part 25 airplanes directly relate to part Start Printed Page 295023 airplanes. The tasking that PPIHWG is working for part 25 airplanes only considered transport category airplane design and operation. The design and operation of part 23 airplanes is different from part 25 airplanes. Therefore, direct adoption of part 25 requirements into part 23 without fully evaluating these operational and design differences could result in lowering the overall safety of part 23 airplanes.

A commenter stated that the proposed policy does not appear to contain new policy material. We disagree. The proposed policy provides new criteria, which has not been applied to all part 23/CAR 3 airplanes.

A commenter wrote that they oppose this policy as it proposes to require new designs to prevent intentional prohibited operations. We disagree. This policy is not requiring new designs to prevent intentional prohibited operations, rather the policy is providing certification considerations for part 23/CAR 3 airplanes that have in-flight beta capability.

A commenter stated that the policy is for regulations that have not been issued or approved. We disagree. The rules applicable to this policy are § 23.1155, which was adopted by Amendment 23-7 effective September 14, 1969, and 14 CFR part 21, §§ 21.21(b)(2) and 21.101(b), which were both effective with the basic part 21 dated February 1, 1965. Therefore, the rules in question are more than 30 years old.

A commenter stated that it is unclear if the section “Inadvertent In-Flight Operation” is directed towards existing type certificated airplanes or future type certificated airplanes. Further, the commenter states that the policy can be easily misconstrued as to require a manufacturer to retrofit airplanes to prohibit in-flight beta operations. We disagree in that the section specifically states “For airplanes with a certification basis before Amendment 23-7 that are modified to add in-flight beta capability * * *” Therefore, the section obviously applies to existing type certificated airplanes that are modified.

A commenter said the requirement for the flight manual to contain appropriate operational limitations and consequence statements for in-flight beta operation could not be mandated by policy. We agree, but the policy does not mandate such actions. Rather the policy provides certification guidance, which is reflected when the policy is finalized.

A commenter stated that the beta lock-out systems discussion is unclear; specifically, is it directed towards future type certificated airplanes, existing type certificated airplanes undergoing modification, or existing type certificated airplanes not undergoing modification? Also, the commenter requested clarification of which version of § 23.1155 this section applies; before Amendment 23-7, at Amendment 23-7, or the proposed § 23.1155. Further, the commenter states that if the section applies to the proposed § 23.1155, this policy can not enforce a rule that has not been issued. We agree with the commenter's first comment. Therefore, the beginning of the second paragraph of this section was modified to add qualifiers on which airplanes this section applies. We disagree with the commenter's remaining comments in that there is only one version of § 23.1155, the version at Amendment 23-7, which was the amendment level that adopted the rule. Further, the commenter is incorrect in that this policy is not proposing a rule change.

A commenter requested clarification on who does a system safety analysis. We agree and this section was modified by indicating that the applicant performs the analysis.

The Policy


The National Transportation Safety Board (NTSB) has recommended rulemaking action to amend 14 CFR part 23 to require a means to prevent in-flight operation of the propeller at pitch settings below the flight regime (beta mode). For turbine engine installations, § 23.1155, added by Amendment 23-7, requires that operation of the propeller controls for pitch settings below the flight regime have a means to prevent inadvertent operation. The new requirement recommended by the NTSB would be fundamentally different from the current § 23.1155. Unless the airplane is certificated for such use, beta mode could not occur in-flight, even if intentionally commanded. The Small Airplane Directorate is initiating an ARAC, Aviation Rulemaking Advisory Committee, study to determine whether a rulemaking effort should occur.

The FAA has taken actions to address previously certificated airplanes with in-flight beta capability. A fleet wide review of all turbopropeller powered transport, normal, utility, acrobatic, and commuter category airplanes was performed. As a result of the review, the FAA issued Airworthiness Directives that required applicable Flight Manuals to include an operational limitation with consequence statement for in-flight beta operation.

Also, the safety of future type certificated airplanes, with in-flight beta capability, or currently certificated airplanes, which are being modified to add an in-flight beta capability, should be assessed. This assessment should consider both unintentional and intentional operation of propellers in pitch settings below the flight regime.

Inadvertent In-Flight Operation

Regarding inadvertent operation, as previously mentioned, Amendment 23-7 added a requirement (§ 23.1155) that operations of the propeller controls at pitch settings below the flight regime have a means to prevent inadvertent operation. For airplanes with a certification basis before Amendment 23-7 that are modified to add in-flight beta capability, the provisions of § 21.101(b) should be used to evaluate the possible unsafe nature of inadvertent operation of propellers in the beta regime. If it is determined that such operation is unsafe, the issue may be addressed by showing compliance with § 23.1155.

The nature of the regulatory requirement provided by § 23.1155 allows a subjective, qualitative evaluation for compliance determination. The intent is to prevent inadvertent operation in the beta mode, even if the possibility of inadvertent operation is remote. If an operation or feature of the design can allow in-flight, inadvertent placement of the control below the flight regime, the design does not comply with the regulation. In other words, the design should be evaluated considering the types of operations that will be seen in service. Consider items such as hardware wear modes or maintenance issues that may cause the control to be unintentionally placed or creep into the beta regime over time.

Intentional In-Flight Operation

On all future type certification projects, the Flight Manuals should include the appropriate operational limitations and consequence statement for in-flight beta operation.

Beta Lock-Out Systems

To add an assurance that in-flight beta will not occur, some airplanes have incorporated lock-out systems. These systems remove the ability to do this operation in-flight, even if intentionally commanded. It is important to note that the installation of a beta lock-out system cannot be used instead of the design requirements of § 23.1155 compliance. Also, in some cases, propeller beta operation is used to show compliance with stopping distances in part 23, Subpart B. Under Subpart B, when means other than wheel brakes are used for determining stopping distances, the means must be “safe and reliable.” If beta operation is used to show Start Printed Page 2951compliance with stopping distances, the reliability of a system that would prevent in-flight beta operation must be such that this capability, when required, will be available to comply with Subpart B, and § 21.21(b)(2) or § 21.101(b). With a system safety analysis, the applicant can determine the required reliability level for the beta lock-out system based on the hazard level (for example, § 23.1309 compliance).

Therefore, for new type certificated airplanes that have a beta lock-out system incorporated or previously certificated airplanes that add a beta lock-out system, the applicant should perform a system safety analysis of the installation of this system. This analysis should consider hazards such as the inability to command beta on one engine on a multiengine airplane. For example, if beta is commanded on both engines during land roll-out, but only one propeller goes into beta mode, this might adversely affect ground controllability.

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Issued in Kansas City, Missouri on December 22, 2000.

Marvin R. Nuss,

Acting Manager, Small Airplane Directorate, Aircraft Certification Service.

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[FR Doc. 01-1088 Filed 1-11-01; 8:45 am]